Hard disk drives, which are widely used as a data storage device for computers and like devices, includes a magnetic head for reading user data stored on a magnetic disk or writing user data onto a magnetic disk. The magnetic head is mounted on an actuator that is oscillated by a VCM (Voice Coil Motor). When the magnetic head reads or writes user data, the actuator is driven to move the magnetic head to a specific track (target track) for positioning purposes. Magnetic head positioning control is exercised in accordance with servo information stored on a magnetic disk to move the magnetic head to a specified position. In line with recording density improvement, hard disk drives released in recent years have begun to use an MR (magnetoresistive) head, GMR (giant magnetoresistive) head, or other magnetoresistive device, which produces a magnetoresistive effect, as a read-only read head, and a transducer induction head as a write-only write head. These two heads are mounted on the same actuator but positioned at a predetermined distance from each other.
A plurality of data tracks are concentrically formed on a hard disk or other magnetic disk. Further, servo tracks, which store identification information and burst patterns beforehand, are formed in the radial direction of a magnetic disk. The aforementioned servo information comprises the identification information and burst patterns. The identification information indicates the track address of a data track. The identification information acquired by the read head is used to determine the data track on which the read head or write head is positioned. As the burst patterns, a plurality of burst pattern rows, which differ in signal storage area phase, are employed so that various signal storage areas are arranged at fixed spacing intervals and in the radial direction of a magnetic disk. In accordance with a signal (PES: Position Error Signal) that is generated by the read head depending on the burst patterns, the deviation of the read head or write head from the target data track can be detected.
The servo information is written onto a magnetic disk in a manufacturing process that is performed prior to hard disk drive shipment as a product. For an accurate read/write of user data, the servo information, which serves as the reference, needs to be accurately written. Conventionally, a dedicated device called an STW (Servo Track Writer) was used to write servo information onto a magnetic disk. Recently, however, a self servo write (SSW) method for enabling a hard disk drive to perform a servo write by itself has been proposed and put to practical use (refer to Patent Documents 1 and 2).
[Patent Document 1]
Japanese Patent Laid-Open No. 11-1999 (pages 9 and 10)
[Patent Document 2]
Japanese Patent Laid-Open No. 2002-8331 (page 3)
The conventional self servo write method, however, cannot easily determine the absolute track pitch (the distance between the track center of one track and the track center of the next adjacent track). This problem can be solved, for instance, by performing a self servo write onto the area between the inside diameter (ID) and outside diameter (OD) sections at an appropriate track pitch, regarding the obtained radial distance of the magnetic disk as an absolute length, and performing a self servo write again in such a manner as to acquire a track pitch having a desired length.
However, the use of the above method causes problems, which will now be described. If, for instance, the head width of the read head is significantly narrow as compared to a written track pitch, a deadband arises. The deadband is a region where changes in all the burst patterns formed in accordance with a track pitch cannot be read by the read head. Servo control within such a deadband becomes unstable.
On the other hand, if the head width of the write head is significantly wide as compared to a written track pitch, the write head writes data not only on the target track but also on a track adjacent to the target track. It means that the data on such an adjacent track can be overwritten.
Further, a self servo write needs to be performed twice on the entire magnetic disk surface. As a result, the servo information write process requires an increased amount of time, thereby decreasing the efficiency of hard disk drive manufacture.
The present invention is made to solve the foregoing technical problems, and has for its object to write servo information onto recording media at an improved track pitch even when the self servo write method is employed. It is a further aspect of the present invention to reduce the time required for a servo information write according to the self servo write method.